1. Field of the Invention
The present invention relates to an apparatus that securely distributes encrypted digital contents (hereinafter also referred to as “electronic media”) from a server to a client over a network, and also provides a mechanism that prevents unauthorized use of digital contents. The apparatus can thereby be regarded as having a part of the Digital Rights Management (DRM) function.
2. Description of the Prior Art
When electronic media are being distributed over a network, methods of preventing the media being copied include channel encoding in which the distribution channel from the server to the client is encrypted to prevent it being tapped by a third party, and content encrypting in which the content is encrypted to prevent unauthorized use. There are various algorithms for performing the encryption, such as DES, Triple DES, AES, MULTI, RC5, and MISTY. Decryption by exchanging a key is performed by the use of a key on the basis of the RSA public-key cryptosystem or other such methods.
With the above methods, however, there is a risk that some means may be used to crack a client's application software or operating system, or that when bit-strings flowing through a data bus are measured by a measurement device, the decryption key, or the raw data produced by decrypting the electronic media, may be stolen.
With the object of recording data that makes it difficult for an unauthorized user to acquire an encryption key, Unexamined Patent Application Publication 2003-69551 discloses an encryption apparatus, and method that records first encryption data and a first encryption key encrypted using a second encryption key on an information storage medium, holds the second encryption key encrypted using a third encryption key and holds the third encryption key.
Thus, the above disclosure is somewhat effective in preventing unauthorized copying by using a plurality of encryptions to protect the entire storage medium. However, the above-mentioned constitution requires considerable processing to encrypt and decrypt the electronic media. Carrying out the processing requires the use of devices that are capable of high-speed processing, which makes it costly. Moreover, because of the encryption keys that are used as the encryption means being generated by a program put in a storage medium, the above-mentioned apparatus and method merely make it more complicated to obtain encryption keys and, in addition, do not adequately prevent unauthorized copying of the electronic media, and as such, do not provide sufficient security for the information concerned.
In view of the shortcomings of the prior art described above, the object of the present invention is to provide an electronic media communication apparatus which is equipped with means for keeping an encryption key secret in a logic programmable device as a circuit and in which the decryption algorithm is also built-in as a circuit in the logic programmable device to thereby enable hardware-based decryption.